The present invention relates to a ceramic porous membrane, a ceramic porous body and a method of manufacturing the membrane. More particularly, it relates to a ceramic porous membrane comprising ceramic particles and ceramic sol particles as a binder for the ceramic particles, and a method of manufacturing the ceramic porous membrane.
Ceramic porous membrane is used in, for example, filters for solid-liquid separation. As compared with polymeric membranes which are used for the same purpose a ceramic porous membrane is useful in that since physical strength and durability are excellent, reliability is high, and that since corrosion resistance is high, deterioration is small even if washed with acid or alkali, and that it is possible to finely control pore diameter which determines filtration ability.
Conventionally, filtration ability has been secured by further forming a porous membrane having small pore diameter on, for example, a surface of a substrate comprising a porous material having relatively large pore diameter.
For example, Japanese Patent Application Laid-Open No. 63-274407 discloses a method of manufacturing a porous membrane, which comprises adding ceramic sol to particles which constitute a ceramic membrane, and sintering the resulting mixture at 1,200xc2x0 C.
In each of the above-described methods, ceramic particles are sintered to each other, or ceramic particles and ceramic sol particles are sintered, at a high temperature to form neck between particles, thereby obtaining further strong bond.
Therefore, unless the particles are sintered at a high temperature of at least 1,200xc2x0 C., ceramic porous membrane having practically usable strength cannot be formed. Further, sintering at such a high temperature involves disadvantages that electric charges are high, and a setter to be used for the sintering must be constituted of a refractory material which can be used at a high temperature, such as silicon carbide. Thus, expensive and specific facilities must be provided, and equipment investment is necessary, resulting in a high cost.
In view of the above problems inherent in the prior art, the present invention has been made, and therefore an object of the invention is to provide a ceramic porous membrane and a ceramic porous body which can be molded at a temperature at which any specific refractory facilities are not required, and which has practically usable strength.
Another object of the present invention is to provide a method of manufacturing the ceramic porous membrane.
According to one aspect of the present invention, there is provided a ceramic porous membrane comprising ceramic particles and ceramic sol particles (with the exception of TiO2 sol particles), the ceramic particles and the ceramic sol particles are kneaded to obtain a kneaded product or a slurry, the kneaded product or the slurry being sintered at a lower temperature, wherein the ceramic sol particles have an average particle diameter of ⅕ or less of an average particle diameter of the ceramic particles, and the ceramic sol has a solid content of 1 to 30% by weight based on the weight of solid content of the ceramic particles.
The ceramic porous membrane of the present invention can use, as the ceramic sol particles, ceramic sol particles other than ZrO2, ceramic sol particles other than SiO2, or ceramic sol particles other than a mixture of ZrO2 sol particles and SiO2 sol particles.
The ceramic sol particles preferably contain at least one of Al2O3.SiO2, and MgO.Al2O3.
Further, according to the present invention, there is provided a ceramic porous body, wherein the ceramic porous membrane is formed on the surface of a porous substrate.
According to another aspect of the present invention, there is provided a method of manufacturing a ceramic porous membrane, which comprises adding ceramic sol particles (with the exception of TiO2 sol particles) having an average particle diameter of ⅕ or less of an average particle diameter of ceramic particles to the ceramic particles such that the solid content of the ceramic sol is 1 to 30% by weight based on the weight of a solid content of the ceramic particles, mixing the particles, depositing or molding the resulting mixture, and heat treating the resulting film or molded product at 300xc2x0 C. or less under aqueous vapor atmosphere, thereby fixing the ceramic particles.
According to further another aspect of the present invention, there is provided a method of manufacturing a ceramic porous membrane, which comprises adding ceramic sol particles (with the exception of TiO2 sol particles) having an average particle diameter of ⅕ or less of an average particle diameter of ceramic particles to the ceramic particles such that the solid content of the ceramic sol is 1 to 30% by weight based on the weight of a solid content of the ceramic particles, mixing the particles, depositing or molding the resulting mixture, and heat treating the resulting film or molded product at 300 to 700xc2x0 C. under air (ambient) atmosphere, thereby fixing the ceramic particles.
In the above manufacturing method of the present invention, the ceramic sol particles preferably contain at least one of SiO2, ZrO2, Al2O3.SiO2, and MgO.Al2O3.